Polymers containing hydroxamate groups have been known to be particularly useful for the flocculation of red muds produced in the Bayer process, see U.S. Pat. No. 4,767,540. These polymers are generally produced by reacting aqueous solutions of the polymers, e.g. polyacrylamide, with hydroxylamine salts. When the molecular weight of the polymer being hydroxamated is of such a value that the polymer performs at its best in the flocculation application, it has hitherto been in the form of a highly viscous gel. The high viscosity of the gel causes major handling problems both during and after hydroxamation since high viscosity fluids are extremely difficult to transfer from one vessel to another e.g. from reactor to storage, from storage to shipment container and from shipment container to application. The viscosity of such a gel is particularly high when the molecular weight of the polymer is high, i.e. over about 1,000,000.
Furthermore, it is customary for polymers of such high viscosities to be pre-diluted, usually in water, before they are used, so that they may be more easily mixed into the substrate which is to be subjected to flocculation. The high viscosity of hydroxamated polymer gels makes this a difficult process to undertake and often requires the use of specialized and expensive equipment. These inherent limitations in such gels necessarily means that the solids content of such gel products must be kept as low as possible in order to maintain the viscosity at a practical level, i.e. the lower the solids content, the lower the viscosity. The shipment costs of low solids solutions of polymer, however, are significantly higher because of the dilution.
In the case of conventional acrylamide polymers, the viscosity problems have been largely overcome through the development of high solids water-in-oil microdispersions, i.e. such forms as microemulsions, emulsions, microsuspensions, and as used herein, such term is meant to include said forms. As small micelles, the high viscosity polymers, while still being, in effect, gels themselves, are nevertheless, more easily dissolved in the substrates to which they are added in use. Thus, where a polymer solution at high solids is a stiff gel, a microdispersion of the same gel is more easily handled and used due to its lower viscosity.
Attempts have been made to create stable microdispersions of hydroxamated polymers in the past, see U.S. Pat. Nos. 4,587,306; 4,767,540 and 4,868,248. Due to the complexities of performing the hydroxamation reaction in this product form, however, it has not been previously possible to satisfactorily accomplish this goal. The problems attendant such hydroxamation reactions include poor incorporation of the hydroxamate functionality, poor stability of the emulsion, i.e. phase separation after relatively short periods of standing, insolubilization of the polymer, molecular weight degradation etc.
U.S. Pat. No. 4,587,306 to Vio discloses a method for preparing hydroxamated polymer emulsions from polyacrylamide backbones of low molecular weight, e.g. 4000 or below. There is no evidence, however, that the material produced was a true polymer dispersion in oil or, in fact, even an oil-in-water type. It is known that the problem of reacting a polymer backbone with a reagent becomes more acute when the molecular weight of the polymer is high. Attempts to produce, by the method taught in U.S. Pat. No. 4,587,306, both low and high molecular weight, stable, gel-free, water-in-oil hydroxamated polymer emulsions have shown that the incorporation of hydroxamate functionality is much lower (and insignificant) than shown therein for the claimed low molecular weight polymers. Furthermore, at the elevated reaction temperatures thereof, e.g. 70xc2x0 C., it is very difficult to form a stable emulsion if, in fact one can be formed at all. Indeed, the examples below show that a stable, gel-free high molecular weight, hydroxamated polymer emulsion was not formed under the reaction conditions of this patent at room temperature or at 70xc2x0 C. Thus, it is clear that the process of the ""306 patent is not suitable for the preparation of the microdispersions claimed herein. A further distinction worth noting is that the mole ratio of KOH to hydroxylamine hydrochloride used by the process of U.S. Pat. No. 4,587,306 is only 0.78, i.e. the hydroxylamine is only partially neutralized and the reaction is therefore conducted under acidic conditions which limits the rate of the reaction and necessitates the use of extreme temperatures which further causes the formation of unstable products.
In U.S. Pat. No. 4,767,540 there is disclosed a method for the production of hydroxamated polyacrylamides in which there is purported to be produced a stable emulsion of hydroxamated polyacrylamide. However, attempts to duplicate the procedure of this patent have proven to be less than successful in that the resultant products are not stable, gel-free, water-in-oil microdispersions, see Examples 34 and 35, below.
U.S. Pat. No. 4,868,248 discloses that emulsions of hydroxamated polymers can be produced; however, the patentee fails to disclose any specific example to the production of such a polymer. Both methods described for preparing the polymers thereof are solution-based and no water-in-oil microdispersions are shown.
Accordingly, the search continues for a method for the production of stable, gel-free microdispersions of hydroxamated vinyl polymers, i.e. one in which the structural integrity of the microdispersion remains in tact and is pourable.
Stable, gel-free microdispersions of hydroxamated vinyl polymers of the water-in-oil type with micelle sizes of the discontinuous phase ranging from about 0.02 to 50 microns and having molecular weights of over about 1,000,000 have been produced. The microdispersions are gel-free and are readily dispersed in water by self-inversion.
By the use of the term xe2x80x9cstable, gel-freexe2x80x9d microdispersions as used herein, is meant that the microdispersion remains as two distinct phases i.e. continuous and discontinuous phases, after a reasonable period of time e.g. up to about 9 months and is pourable or free flowing. That is to say, a xe2x80x9cgel-freexe2x80x9d system as referred to herein, is a microdispersion which has not undergone detrimental agglomeration of the micelles of the discontinuous phase such that the microdispersion is not free flowing. Although such a microdispersion may contain gelled polymer, as long as the micelles of gelled polymer are prevented from agglomerating into large detrimental clumps, the microdispersion is still pourable and applicable for its intended use.
Hydroxamated vinyl polymers in microdispersion form are produced by reacting a water-in-oil microdispersion comprising a continuous phase and a discontinuous phase containing a precursor vinyl polymer with neutralized hydroxylamine and, preferably, an excess of base. The process does not require elevated temperatures or extended reaction times, contrary to prior art procedures.
The instant invention relates to stable, gel-free, water-in-oil microdispersions comprising a continuous phase of a suitable hydrocarbon oil and an emulsifier and a discontinuous phase of an aqueous solution of an hydroxamated vinyl polymer having a molecular weight of over about 1,000,000.
The invention also relates to a method of producing stable, gel-free, water-in-oil microdispersions of hydroxamated vinyl polymers comprising reacting 1) a water-in-oil microdispersion comprising a continuous phase of a suitable hydrocarbon oil and an emulsifier and a discontinuous phase of micelles of an aqueous solution of a precursor vinyl polymer with 2) neutralized hydroxylamine and, preferably, an excess amount of base.
Exemplary of the vinyl polymers useful in the present invention are those which contain a pendant functionality which will react with hydroxylamine, i.e. those produced from acrylic, methacrylic, crotonic acids etc.; acid esters such as methyl acrylate, ethyl acrylate, t-butyl acrylate, and the corresponding methacrylate esters, dimethylaminoethyl methacrylate; dimethylaminoethyl acrylate; and quaternary salts thereof; methyl crotonate, etc.; polymers of maleic anhydride and esters thereof, and the like; nitrile polymers such as those produced from acrylonitrile etc.; amide polymers such as those produced from acrylamide, methacrylamide and the like. Carboxymethylcellulose esters, starch esters, xanthates, etc. may also be used. The polymers may be also crosslinked such as by reaction with a cross-linking agent, e.g. methylenebisacrylamide, divinylglycol, etc.
The above vinyl monomers may also be copolymerized with each other or with any other anionic, cationic or non-ionic monomer, or mixture thereof.
Any emulsifier which is effective such as to provide the proper average diameter of micelles and to prevent the resultant vinyl polymer micelles, which generally range in average diameter size from about 0.02 to about 50 microns, preferably from about 0.1 to about 10 microns, and more preferably from about 0.2 to about 5 microns, from detrimentally agglomerating can be used to prepare the novel compositions hereof. These emulsifiers are such that the microdispersion of the hydroxamated vinyl polymer remains free flowing i.e. does not experience the agglomeration of the gelled polymer solution micelles such that it becomes incapable of flowing e.g. in the worst case scenario, solidified as a gelled mass.
Suitable emulsifiers useful for these purposes in the preparation of such water-in-oil microdispersions of the vinyl polymers to be hydroxamated include the ethoxylated fatty amines; the alkanolamides of fatty acids; imidazole-fatty acid reaction products; alkanolamine-fatty acid condensation products; sorbitan fatty esters, and the like. Suitable emulsifiers should be chosen to result in the formation and maintenance of the polymer micelles ranging in size from about 0.02 to about 50 microns.
It may be advisable to add additional amounts of the same or different emulsifers to the emulsion to be hydroxamated so as to maintain the integrity thereof during the hydroxamation procedure i.e. the emulsion must be kept stable and gel-free during and after the hydroxamation reaction.
The vinyl polymers of the water-in-oil microdispersions e.g. emulsions, claimed herein have weight average molecular weights of at least about 1,000,000, preferably, over 5,000,000 more preferably, over 10,000,000.
Any known hydrocarbon oil may be used in forming the microdispersion of polymers to be hydroxamated including isoparaffinic, normal or cyclic hydrocarbons such as benzene, xylene, toluene, fuel oil, kerosene, odorless mineral spirits, and mixtures thereof.
The ratio of aqueous phase to hydrocarbon phase in the microdispersions should range from about 0.5 to about 3:1, and usually approximates 2:1.
The procedure for forming the precursor vinyl polymer microdispersion is well known in the art and may be obtained from any of the following U.S. patents which teach the production of such microdispersions, i.e. U.S. 4,521,317 (Candau) 4,147,681 (Lim) etc.
The precursor microdispersion, and/or the final hydroxamated polymer microdispersion, may be treated to remove water and/or oil by any suitable means, e.g. distillation so as to increase the polymer solids content. The polymer solids content, before or after dehydration may range from about 5% to about 70%, preferably from about 10% to about 60%, based on the total weight of the microdispersion.
The precursor polymer microdispersion is treated with hydroxylamine to hydroxamate the polymer in accordance with the process of the present invention as discussed below. The hydroxylamine is usually employed as a salt and is preferably neutralized with base before or during the hydroxamation reaction.
Suitable hydroxylamine salts include the sulfates, sulfites, phosphates, hydrochlorides, acetates, propionates and the like. The pH of the hydroxylamine solution is adjusted to about 3-14, however, it is preferred that the pH be maintained over about 6.0, and more preferably over about 11.0, by means of the addition of base e.g. NaOH, to the solution.
The degree of hydroxamation, i.e, the concentration of hydroxamate units in the polymers useful herein, may range from about 1 to about 100 mole percent, preferably from about 5 to about 75 mole percent and, most preferably, from about 10 to about 50 mole percent.
The hydroxylamine salt is preferably used in conjunction with an excess (on a molar basis) of base such as potassium hydroxide, sodium hydroxide, ammonia, lime, etc. The preferred base is sodium hydroxide, and preferably more than about 5% molar is used, based on the reactive groups of the precursor polymer.
The hydroxamation reaction may be conducted at low temperature i.e. from about 10xc2x0 C. to about 90xc2x0 C., preferably from about 15xc2x0 C. to about 60xc2x0 C., more preferably about 15xc2x0 C.-40xc2x0 C.
In a preferred embodiment, a stabilizer suitable to stabilize the vinyl polymer against degradation due to the presence of hydroxylamine is added to the hydroxylamine reactant. Suitable stabilizers include water-soluble alkali metal, alkaline earth metal or ammonium thiosulfates; 2-mercaptolhiazoles; 2-mercapthothizolines; thiuram disulfides; thioureas; mercaptoalkanols; see U.S. Ser. No. 07/074,475 and U.S. Ser. No. 07/704,479, both filed May 23, 1991 and now U.S. Pat. Nos. 5,227,146 and 5,141,730, respectively.
The hydroxylamine or its salt, excess base and, preferably, the stabilizer is added to and reacted with the precursor vinyl polymer microdispersion in the form of an aqueous solution or as an emulsion. Preferably, the compounds are used in the form of a solution. The emulsion may be formed by adding an aqueous solution of the compounds to any of the oils described above in the presence of an emulsifier such as those disclosed above. The same emulsifier used to form the vinyl polymer microdispersion to be hydroxamated may be used in the formation of the hydroxylamine emulsion charge. A different emulsifier or mixture of emulsifiers may also be used. It is critical, however, that the result of the presence of the emulsifier(s) is such that the hydroxylamine solution goes into the aqueous phase of the precursor microdispersion and the final hydroxamated vinyl polymer dispersion is stable and gel-free, as discussed above. Homogenization of the aqueous solution with the oil and emulsifier is preferred; however, a useful cruder emulsion may be attained by merely stirring said components. Alternatively, the hydroxylamine solution of hydroxylamine, excess base and stabilizer can be added directly to the precursor vinyl polymer microdispersion to which may be added, additional oil and emulsifier, with stirring as long as the above discussed criteria are met. Still further, each individual component, i.e. the hydroxylamine, the excess base and the stabilizer, may be formed into individual emulsions and added as such to the precursor vinyl polymer microdispersion.
The degree of hydroxamation is controlled by the ratio of the added hydroxylamine reagent to the ratio of the precursor vinyl polymer back-bone reactive groups, as is known in the art. The instant method results in a very high conversion of hydroxylamine. The degree of hydroxamation may be determined by carbon 13 Nuclear Magnetic Resonance spectroscopy and is quoted herein in mole percent. The hydroxamated vinyl polymer molecular weights may be determined by ascertaining the viscosity of a dilute polymer solution in molar sodium chloride. The Solution Viscosity (SV), as used herein, is determined on a 0.1%, based on the precursor polymer, polymer solution at 25xc2x0 C. using a Brookfield viscometer with UL adapter at 30 rpm for SV greater than 10 using the following relationship: SV=exp. {In 30 rpm viscosityxe2x88x920.162} and at 60 rpm for SV less than 10 and as quoted in mPa.s. Hydroxamated vinyl polymer water-in-oil microdispersions having Solution Viscosities of over about 2.0 can be produced by the process of this invention.
The hydroxamated vinyl polymer water-in-oil microdispersions of this invention can be dissolved directly in water to form aqueous solutions which may be used as, for example, flocculants. Additionally, a breaker emulsifier may be added to the microdispersions or dilution water to which the microdispersion is added to help invert the microdispersion and thereby improve the dissolution characteristics, if necessary or desired. Additionally, the hydroxamated vinyl polymer may be isolated from the microdispersion in the form of a dry powder, such as by precipitation in a non-solvent or by drying.